Solenoids have been used to provide a number of functions in automotive applications including, but not limited to use in automatic transmission systems and the like. For example, the control system of an automatic transmission is typically hydraulically operated through the use of valves which direct and regulate the supply of pressure. This hydraulic pressure control causes either actuation or de-actuation of frictional members for affecting gear changes in the transmission.
More recently, automatic transmission designs have included adaptive control systems which utilize electrically operated solenoid-actuated valves for controlling various fluid pressures. However, current solenoid-actuated valve designs have their shortcomings. For example, vibrationally-transmitted impact noise during shifting results in a chattering effect from solenoid actuation. This chattering can be a result of the pulse width modulated (PWM) electronic drive signal which actuates the solenoids. This can occur under step shifting conditions in which the solenoid ramps from 0 to 100 percent duty cycle or vice versa. The vibrational energy generated is at the excitation PWM frequency, as well as the higher order multiple of the drive frequency. This vibrational energy directly transmits from the solenoid through its mounting interface into the transmission housing. The presence of excessive noise and vibration levels is typically undesirable and potentially leads to customer dissatisfaction.
One approach to overcoming this problem is found in commonly-assigned U.S. Pat. No. 5,651,391, the entire disclosure of which is expressly incorporated herein by reference, which discloses a solenoid-actuated valve assembly with reduced noise characteristics. More specifically, a rubber retainer and steel retainer secure the valve within a manifold, wherein the rubber retainer absorbs longitudinal vibrations. A plurality of rubber gaskets surround the body of the valve and prevent metal-to-metal contact between the valve body and the manifold for cushioning lateral vibrations of the valve. However, this approach uses a unitary rubber retainer that extends along most of the length of the solenoid assembly, with corresponding raised portions for shrouding the top portions of the respective individual solenoids. This approach is wasteful in that excessive material must be used to manufacture the rubber retainer, as well as being fairly inadaptable, in that it cannot be easily modified should the solenoid assembly layout design be changed later.
Therefore, there exists a need for new and improved pulse width modulated solenoid systems having low noise characteristics.